Two speed incremental drive

ABSTRACT

936,441. Ratchet gearing. INTERNATIONAL BUSINESS MACHINES CORPORATION. Jan. 2, 1962 [Jan. 9, 1961], No. 94/62. Addition to 932,113. Classes 80 (2) and 80 (3). In a two-speed ratchet gear, two pawls 26a, 26b on pawl actuating arms 14a, 14b are driven in opposite phase in cyclic manner to move the pawls into and out of engagement with parallel sided notches 30 in a ratchet 28a, 28b, means being provided to latch one pawl arm to prevent that pawl moving the ratchet, whereby the ratchet is driven at a lower speed when the pawl arm is latched. In a punched card feed mechanism, a driving-shaft 12 carries two cams 13a, 13b, 180 degrees out of phase, which oscillate a forked pawl lifting member 34 and pawl arms 14a, 14b, respectively. The lifting member arms 36a, 36b are arranged to lift the pawls out of the notches on the return stroke. A pawl may be held from engagement, to provide a half-speed drive, by electromagnet 41 having a &#34; hold &#34; coil 41a and a &#34; bucking &#34; coil 41b, under which condition the pawl enters a notch to prevent back-running but does not drive the ratchet. In a second embodiment, Fig. 2, (not shown), the pawls are arranged to impart step-by-step motion to linearly moving notched rods.

May 5,1964 M. J. WHITE TWO SPEED INCREMENTAL DRIVE 3 Sheets-Sheet 1Filed Jan. 9, 1961 v QE INVENTOR. MALCOLM J. WHITE Z/ Q/ 7 ATTORNEY May5, 1964 M. J. WHITE TWO SPEED INCREMENTAL DRIVE 3 Sheets-Sheet 2 FiledJan. 9, 1961 N QE May 5, 1964 M. J. WHITE TWO SPEED INCREMENTAL DRIVE 3Sheets-Sheet 3 Filed Jan. 9, 1961 FIG. le

United States Patent Oflice 3,131,570 Patented May 5, 1964 3,131,570 TWGSPEED ENCREMENTAL DRIVE Malcolm 5. White, Los Gatos, Calif., assignor toInternational Business Machines Corporation, New York, N.Y., acorporation of New York Filed Jan. 9, 1961;, Ser. No. 81,481 3 Claims.(Cl. 74-425) This invention relates in general to incremental drivemechanisms and relates more particularly .to such mechanisms which arecapable of being driven at one or the other of two speeds.

There are numerous applications where a variable speed incremental drivemechanism is required, such as in punched card feeding mechanisms and indrives for printer carriages in which the carriage must be accuratelypositioned and stopped at each printing station and must be rapidlymoved between adjacent printing stations. In copending application,Serial No. 862,922, now Patent Number 3,078,732, Gunter H. Schacht andLawrence A. Wilson, assigned to the same assignee as the presentapplication, there is disclosed an incremental drive mechanism whichprovides incremental movement in either of two directions. Theincremental movement available with the above mentioned inventionincludes incremental motion in either of two directions and anoscillatory motion comprising alternate increments of movement inopposite directions. Basically, the above incremental drive mechanismincludes a rotating shaft which drives a pair of cams, with one of thesecams driving two spring loaded pawl actuating arms back and forth inopposite phase. Each of these pawl actuating arms is pivoted at one endand is connected at the other end to a pawl member so that the pawlmembers move back and forth in response to movement of the pawlactuating arms by the cam. The other end of each pawl engages notches ina ratchet which is connected to the load to be driven, so that movementof the pawl while it is engaged with a notch imparts driving movement tothe load. The other cam on the rotating shaft drives a pair of springloaded pawl lifters which guide the ends of the respective pawls in andout of engagement with the notches at the proper times in the drivecycle.

The above structure also includes control means for selectivelydisengaging one or the other pawl actuating arms to selectively latch anarm out of driving operation. With one pawl actuating arm latched out ofengagement, the other or driving pawl actuating arm is moved into andout of driving engagement with the notches in the ratchet to produceincremental movement of the notches and attached load in one direction,the direction of movement being determined by which of the two pawlactuating arms is latched.

One of the significant features of the above described incremental drivemechanism is the use of notches in the ratchet which have substantiallyparallel sides for a substantial portion of the notch depth beforebecoming rounded at the bottom of the notch. This use of parallel sidesin each notch results in the retention of the pawl member in the notchfor a considerably longer portion of the drive cycle than would resultwere conventional notches having more rounded sides utilized. By somaintaining the pawls in the notches for a maximum portion of the drivecycle, there results a maximum return of kinetic energy from thedecelerating load and other parts of the drive through the pawls to thespring loaded pawl actuating arm. This retention of the pawl members inthe notches insures that the kinetic energy involved in decelerating theload is returned'through the ratchet and pawl to the spring which isurging the pawl actuating arm in one direction. Thus, the energy fromthe deceleration of the load in one portion of the cycle is returned tothe pawl actuating arm spring where it is stored and then utilized inthe next portion of the cycle to urge the pawl actuating arm and pawlforward to perform the subsequent acceleration stroke.

Broadly, the present invention contemplates apparatus utilizing some ofthe features of the above described structure to produce controllabletwo-speed incremental drive in one direction. In accordance with thepresent invention, a drive shaft drives a pair of cams, one of whichdrives a pair of pawl actuating arms in opposite phase with respect toeach other. Each pawl actuating arm is pivoted at one end and isconnected at the other end to a pawl member which is cngageable withnotches in a ratchet connected to the load to be driven. The two pawlmembers are disposed with respect to the ratchet so that they drive theratchet during opposite halves of the drive cycle. Where the ratchet isin the form of a wheel having notches around the periphery thereof, thepawls are located at points apart on the circumference of the ratchetwheel and are so disposed and driven that when one pawl is commencingits portion of the drive cycle the other pawl has just completed itsportion of the drive cycle and is returning to the position at which itwill resume driving. Where the ratchet is in the form of an elongatedmember having notches spaced along the length thereof, the pawls aredisposed to engage adjacent portions of the notches, with one pawl justcompleting its portion of the drive cycle when the other pawl is justcommencing its portion of the drive cycle.

Control means are provided for selectively latching one or both of thepawl actuating arms out of driving engagement with the ratchet. With onearm latched out of driving engagement with the ratchet, the non-latchedarm will drive the ratchet in its usual fashion, but the ratchet will bedriven only during the half cycle corresponding to the unl-atched arm,and the pawl which is connected to the latched arm will merely rock inand out of engagement with a ratchet notch without imparting any drivingmovement thereto. Under these conditions, with one pawl actuating armlatched, the non-latched arm drives the ratchet and connected load at agiven speed. With both pawl actuating arms unlatched, the ratchet isdriven alternately during half cycles of the drive cycle by each pawl,so that the average speed is twice the average speed at which theratchet is driven with one arm latched. Thus the device provides acontrollable two-speed incremental drive mechanism, which provides afirst speed of operation in which one half of the drive cycle is.utilized for driving and the other half is available for other types ofoperations on the stationary load, and provides a second speed ofoperation which is double the first speed with out requiring any higherspeed operation of any of the elements of the driving system.

Objects and advantages of the present invention will be apparent fromthe following description when read in connection with the accompanyingdrawings in which:

FIG. 1 is a perspective View illustrating one en1bodi ment of thepresent invention in connection with incremental drive for a cardfeeding mechanism;

FIG. 2 is a perspective view illustrating an alternative embodiment ofthe invention for driving a ratchet member in the form of an elongatedstrip having a plurality of notches therein;

, FIGS, la to lh are fragmentary views of portions of the ratchet andpawls illustrating representative positions of these elements indifferent portions of the drive cycle.

Referring to FIG. 1 by character of reference, there is shown oneembodiment of the present invention for imparting incremental motion ateither of two speeds to a card member 11 such as a punched card. It isassumed that it is desired to drive card 11 in a given direction ateither of two speeds in incremental steps corresponding to the width ofa column on the card. In the assumed application of the invention to acard punching device, the first speed may be utilized to drive the cardto position successive punch positions at the punch station, while thesecond speed may be utilized to drive the card when the punching iscompleted (card eject) or when large fields of the card are not to bepunched (skip punc Also, in a combined card punch-card reader device,the second speed may be utilized to drive the card through the readingstation where a higher card velocity is permissible. The energy fordriving card 11 may be supplied from a suitable motive power source suchas a continuously running motor (not shown) which drives a drive shaft12 extending through a base block 10. A pair of cams 13a and 13b areconnected to one end of drive shaft 12. The inner cam 13b moves a pairof pawl actuating arms 14a and 14b by means of rollers 15a and 1512,respectively, which are coupled to these actuating arms and which rideon the surface of cam 13b. Actuating arms 14a and 14b are pivoted injournal members 16a and 1612 respectively, and each of these arms isurged toward cam 13b by associated spring members 18a and 18b. Springs18a and 18b are adjustably connected to mounting blocks 19a, 1912 by setscrews 21a and 21b.

The upper ends of pawl actuating arms 14a, 14b opposite to their pivotedends are connected to spring pawl members 26a, 2611 respectively. Pawlmembers 26a, Zfib may be of any suitable type, but preferably each is inthe form of an elongated spring which is bent into a generai U shape andwhich is securely connected at one end to its associated pawl actuatingarm. The other end of each or" spring members 26a, 26b is adapted toengage the notches in a notched ratchet which is shown in the embodimentof FIG. 1 as a pair of wheels 28a, 28b having a plurality of notches 30.Wheels 23a, 28b have their corresponding notches aligned but are spacedfrom each other to permit pawl lifters to move thereoetween to disengagethe pawls from the notches, as will be discussed more in detail below.Wheels 28 drive a shaft 29 which is journaled in block and connected toa card fcedroll 31. Card 11 is driven by the pressure of a spring loadedidler wheel 32 which works against the intermittently rotating feedroll31.

Outer cam 13a moves a pawl lifting member 34 which is adapted toalternately lift the spring pawls out of a notch 30 in notched wheels28. Pawl lifter 34 is pivoted at a journal 35 and is provided withprojecting fingers 36a, 3612, which extend between wheels 28a, 28b toengage the ends of the associated pawls 26a, 26b. The cammed end of pawllifter 34 is maintained in contact with the surface of cam 13a by aspring 340 which is connected to a stud 34d secured to base 10.

A pair of control magnets 41, 42 are provided on base 10 forcontrollably latching the pawl actuating arms 14a, 14b. Control magnets41, 42 may be of any suitable type, but preferably they are the typehaving magnetic pole faces which touch or are closely adjacent to theassociated pawl actuating arm when that arm is in the positionrepresented by arm 14a in FIG. 1. Control magnets 41 and 42 may be ofany suitable type magnetically, but preferably each is of the typehaving a pair of coils 41a, 41b, 42a, 42b. Coils 41a, 42a, which may betermed the hold coils, are continuously energized and operate to pass aflux through a magnetic circuit including the associated pole pieces andthe pawl actuating arm. With only the hold coil of a given magnetenergized, when the associated pawl actuating arm comes into contactwith the magnet pole face, it will be retained against the pole face, soas to prevent this actuating arm from imparting any driving motion towheel 28. However, when the associated buck coil 41b, 42b is pulsedwhile the arms 14a or 14b are at the pole faces,

the magnetomotive force therefrom opposes or bucks the magnetomotiveforce produced by the associated hold coil to reduce or cancel theeffective flux in the magnetic circuit, thus releasing the pawlactuating arm from the pole face. Under these conditions, with both thehold and the buck coils energized, the pawl actuating arm follows aregular path and is not influenced by the control magnet.

The use of the hold and buck coils discussed above for the controlmagnet has the advantage of permitting very high speed operation of thecontrol without requiring any substantial amounts of energy through thecontrol magnet windings. It will be noted that the control magnets donot perform any work in the sense of attracting or moving the pawlactuating arms. This mechanical work of moving the pawl actuating armstoward the control magnet is performed by cam 1312 through rollers 15a,15b while the work of urging the actuating arms away from the magnet isperformed by springs 18a, 18b. Thus, the coils of the control magnetsare not required to perform any work in the sense of attracting ormoving the pawl actuating arms and hence the magnetic fields utilized inthe magnet to hold the pawl actuating arms may be much smaller thanwould be required if the magnets had to move the arms.

As an alterative to the use of the hold and buck coils in the mannerdescribed above, the following may be utilized. When it is desired tolatch one of the pawl actuating arms out of engagement, the hold coil isenergized as before to retain the pawl actuating arm against the magnetpole face. When an arm is not to be latched out of engagement, the holdcoil is de-energized as the arm nears or touches the pole face and thebuck coil is then energized. This use of the buck coil aids inovercoming the remanent magnetization resulting from the hold coil toinsure that the arm is not retained against the magnet pole face.

The operation of the present invention can perhaps best be understood byreferring to the diagrams 1a through 1e which illustrate the operationwhen only one pawl is driving ratchet 28 and the load is consequentlybeing driven at a first speed which is one half the average speedobtainable when both pawls are driving. Under these conditions, pawl 26bwill be doing the driving and hence pawl 26a will not be effective inthe driving cycle. Thus pawl actuating arm 14a associated with pawl 26awill be held in the latched position by the associated control magnet41. In FIG. 1a, the driving pawl 26b is in slot 30a but is about to belifted therefrom by the associated pawl lifter 36b, while the inactivepawl 26a is about to enter slot 300. In FIG. lb, pawl 2612 has leftnotch 30a under the action of pawl lifter 36b and is about to be drivento the right toward slot 30:). At this time, the non-driving pawl 26a isin slot Site to detent the wheel 28 during movement of a driving pawl26b between adjacent notches. In FIG. 1c, driving pawl 26b isapproaching notch 3%, while non-driving pawl 26a is being moved out ofnotch 300 by pawl lifter 36a.

In FIG. 10', driving pawl 26b has entered notch 30b, while pawl 26a hasbeen lifted clear of notch 300 by pawl lifter 36a. In FIG. 1e, pawl 26bis driving wheel 28 in a clockwise direction to move notch 30b oneincrement in a clockwise direction so that the load connected to wheel28 moves an amount equal to one increment of motion of wheel 28. Duringthis driving of wheel 28 by driving pawl 26b, pawl 26a, of course, isclear of the notches and rides on the surface of the wheel betweenadjacent notches. At the end of the one increment of motion, pawl 26bstarts to leave notch 30b, which notch now occupies the position whichwas occupied by notch 30a in FIGS. 1a, lb and 10. At the same time, thenon-driving pawl 26a enters notch 30d to detent the wheel 28. The nextstep in the drive cycle would then be substantially identical to thatshown in FIG. 3a, except that wheel 28 will have been rotated in acounterclockwise direction one increment of movement so that each of thenotches will be displaced one increment of motion in a counterclockwisedirection.

From the above description, it will be understood that when operating ata first speed, the unlatched pawl drives the ratchet during one half ofthe drive cycle (a drive cycle being considered as one completerevolution of cams 13a, 13b), and the ratchet is stationary during theother half cycle while the pawl whose actuating arm is latched rocks inand out of one of the notches 30. In the assumed application of theinvention to a card punch, the card is advanced one increment ofmovement as the ratchet rotates during the first half of the drivecycle, and the card is stationary for punching during the other halfcycle when the ratchet is not moving.

It will also be apparent from the above description that to providemotion at a second speed which is double that of the first speed, bothpawl actuating arms are unlatched so that each pawl drives the ratchetduring alternate halves of the drive cycle. Thus, pawl 26a, instead ofrocking in and out of a slot as in FIG. 1, will operate in a mannersimilar to pawl 26b to drive ratchet 28 during one half of the cyclewhile pawl 26b drives the ratchet during the other half cycle to producean average speed which is double the speed with only one pawl driving.

It has been mentioned heretofore that the design of the slots in thedriving wheel 28 plays a significant part in enabling the device of thepresent invention to operate at relatively high speeds without excessiveheat generation in the moving parts. The diagrams of FIGS. lf-hillustrate the action of these slots in retaining the spring pawlmembers therein for a maximum length of time, to result in a maximumabsorption of kinetic energy in the system. In the diagrams of FIGS.lfh, wheel 28 is to be moved one increment of movement to the left,similar to the operation shown diagrammatically in FIGS. 1a through 1e.In FIG. 1,, the wheel 28 is shown at rest with pawl member 2612 restingin notch 305. As pawl 26b is driven to the left by arm 14b and cam 13bto accelerate the wheel in a clockwise direction, the pawl exerts apulling force against the left hand edge of slot 39b, as indicated bythe arrow. This action accelerates the ratchet wheel in a clockwisedirection. Under these conditions of acceleration, the cam 13b isdriving the pawl and the associated load, while spring 13b is under verylight compression and hence does not exert any appreciable effect on thesystem.

In FIG. 1h, the system is decelerating, under which conditions the pawl25b rides against the right hand edge of slot 3% and thus exerts a forcetoward the right, as indicated by the arrow. At this time, spring 1312is under increased compression. Under these conditions, spring isabsorbing the kinetic energy of the decelerating mass in the system andkeeps arm 14b against the cam to provide controlled deceleration of theload without excessive heat generation in the system. The substantiallyparallel sides of the notch serve to retain the pawl therein, duringthis deceleration, so that a maximum amount of kinetic energy istransferred to the spring. This energy which is stored in spring 181)during the deceleration cycle will, of course, be returned to the systemto accelerate the pawl actuating arm 14b and pawl 2612 during the nextcycle of movement.

FIG. 2 illustrates an alternative embodiment of the present invention inwhich the ratchet member is in the form of an elongated strip 51 havinga plurality of spaced notches itl therein. Ratchet 51 is connected to asuitable load which is to be driven in incremental steps at either oftwo speeds. For example, rack 51 may drive a printer carriage which isto be moved in increments representing the distance between adjacentprinting positions and which is to be stopped for printing for a shortinterval at each printing station. Under these circumstances, the deviceof the present invention will drive the carriage between printingstations at a first speed during one half of the drive cycle, with onlyone pawl in driving engagement with the ratchet and will maintain thecarriage stationary at the printing station during the other one half ofthe driving cycle. The printing carriage may also be driven at a secondspeed when both pawls are in driving engagement, this second speed beingdouble that of the first speed. This second speed is useful, forexample, when the printing for a given line is completed or when it isindicated that a large field on the printing medium is to be skipped.

In the embodiment of FIG. 2, drive shaft 29 drives a pair of cams 53a,5312 which in turn drive a pair of pawl actuating arms 54a, 54b. Pawlactuating arms 54a, 54b are journaled at 55a, 55b, respectively, andhave the motion of their corresponding cams communicated thereto byrollers 56a, 56b which ride on the surfaces of the cams. Pawl actuatingarms 54a, 54b are urged against cams 53a, 53b by springs 57a, 5712respectively. Cams 53a, 53b are substantially identical in contour, butare mounted on shaft 20 out of phase with each other, so that themotions they impart to the following pawl actuating arms 54a, 54b aresimilarly 180 out of phase with each other. Pawl actuating arms 54a,5412 are provided with spring pawl members 58a, 58b which engage notches50 in rack 51.

Cams 53a, 53b also drive a pair of pawl lifter members 59a, 5% which aredisposed 180 around the cams from their associated pawl actuating arms.Pawl lifters 59a, 5912 are pivoted at points 63a, 63b respectively, andare urged against the surfaces of their associated cams by springmembers 64a, 64b. Pawl lifters 59a, 59!) have roller members 61a, 61b,respectively, which ride against cams 53a, 53b to communicate the motionof these cams to the pawl lifters. The other ends of the pawl liftersare provided with pointed lifting members 62a, 62b which are disposed inthe grooves between the parallel rows of notches in rack 51 so as tolift pawl members 58a, 5811. From a study of FIG. 2 and from thepreceding description of the embodiment of FIG. 1, it will be readilyappreciated that projecting fingers 62a, 62b of the pawl lifters operatein a manner similar to fingers 36a, 36b of the embodiment of FIG. 1 tolift the pawls 5&1, 58b from notches 50.

The apparatus of FIG. 2 is also provided with control magnets 41, 42which function in a manner similar to that described in connection withthe embodiment of FIG. 1 to selectively latch pawl actuating arm 54a,54b out of driving engagement with the notches in ratchet 51.

The operation of the embodiment of FIG. 2 to provide incremental motionof ratchet 51 at either of two speeds in a given direction will beapparent from the drawing and from the preceding description of theoperation of the embodiment of FIG. 1. To drive ratchet 51 at a firstspeed, one or the other of magnets 41, 42 is energized to selectivelylatch its associated pawl actuating arm 54a, 541; out of drivingengagement. Assuming that magnet 41 is energized to latch pawl actuatingarm 54a, pawl actuating arm 54b is driving the ratchet 51 while pawl 58aassociated with latched pawl actuating arm 54a merely rocks in and outof the notches 56 under the action of pawl lifter 5% without impartingany driving movement to ratchet 51. This operation will be substantiallyidentical to that described above for the embodiment of FIG. 1 and showndiagrammatically in FIG. 3, with pawl actuating arm 54!; and pawl 58bdriving the ratchet 51 for one half or the drive cycle, and with theratchet being stationary during the other half of the drive cycle whiledriving pawl 58b is returning to its position to start another drivingstroke.

To provide movement of ratchet 51 at a second speed which is double thatof the first speed, neither of control magnets 41, 42 is energized, sothat both pawl actuating arms 54a, 54b and their associated pawls 58a,5811 are in driving engagement with ratchet 51. Under thesecircumstances, each of pawls 53a, 58b drives ratchet 51 in the samedirection during its half of the drive cycle to produce a resultantaverage velocity of ratchet 51 which is double the velocity impartedthereto with only one pawl driving.

Thus, it will be apparent that I have provided an incremental drivemechanism which is operable at a first speed to provide increments ofmotion at a first speed, with a period between incremental motions inwhich the load device is stationary, and is operable to drive the loadat a second speed which is double that of the first speed. It will alsobe apparent that this two-speed operation is obtained without requiringthat any of the mechanical parts of the driving system (other than theratchet itself) be driven at any higher speed for the second speed thanfor the first speed. In other words, it will be appreciated from thedescription of the embodiments of FIGS. 1 and 2 that all of the elementsof the driving system, including the cams, pawl actuating arms, pawllifters and pawls, operate at the same velocity during both the firstspeed operation and the second speed operation, and it is only theratchet 51 and the attached load whose average speed is varied. Thistype of operation, in which the velocity of the driving components isnot changed for variations in load speed, is a distinct advantage sinceit eliminates many problems which arise from making changes in thevelocity, acceleration or deceleration characteristics of a drivemechanism to provide variable speed drive.

While the invention has been particularly shown and described withreference to preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in the form and detailsmay be made therein without departing from the spirit and scope of theinvention.

What is claimed is:

1. Apparatus for producing incremental motion from a rotating shaftcomprising a substantially circular ratchet having a plurality ofnotches therein, a first pawl and a second pawl adapted to engage saidnotches, a first pawl actuating arm and a second pawl actuating armconnected respectively to said first and second pawls, means including acam driven by said shaft for driving said first and said second pawlactuating arms in opposite phase in a cyclic manner to move said pawlsinto and out of engagement with said notches to rotate said ratchet inincremental steps in one direction at a first speed, means cycliclydriven by said cam for controlling the movement of each of said pawlsinto engagement with one of said notches for a portion of a cycle andfor moving each of said pawls out of engagement with said notches duringa portion of said cycle, each of said notches having substantiallyparallel sides for a substantial portion of the depth thereof so as toretain said pawls therein for a substantial portion of said cycle, andelectromagnetic means for selectively latching one of said pawlactuating arms away from said cam following position to prevent the pawlassociated with the latched one of said arms from moving said ratchetduring the cycle so that said ratchet is driven at a second speed whensaid one actuating arm is latched which is one-half said first speed atwhich said ratchet is driven when said one actuating arm is not latched.

2. Apparatus for producing incremental motion from a rotating shaftcomprising an elongated ratchet having a plurality of notches therein, afirst pawl and a second pawl adapted to engage said notches, a firstpawl actuating arm and a second pawl actuating arm connectedrespectively to said first and second pawls, means including a camdriven by said shaft for driving said first and said second pawlactuating arms in opposite phase in a cyclic manner to move said pawlsinto and out of engagement with said notches to move said ratchet inincremental movement in one direction at a first speed, means cycliclydriven by said cam for controlling the movement of each of said pawlsinto engagement with one of said notches for a portion of a cycle andfor moving each of said pawls out of engagement with said notches duringa portion of said cycle, each of said notches having substantiallyparallel sides for a substantial portion of the depth thereof so as toretain said pawls therein for a substantial portion of said cycle, andelectromagnetic means for selectively latching one of said pawlactuating arms to prevent the pawl associated with the latched one ofsaid arms away from said cam following position from moving said ratchetduring the cycle so that said ratchet is driven at a second speed whensaid one actuating arm is latched which is one-half said first speed atwhich said ratchet is driven when said one actuating arm is not latched.

3. Apparatus for producing incremental motion from a rotating shaftcomprising a ratchet having a plurality of notches therein, a first pawland a second pawl adapted to engage said notches, a first pawl actuatingarm and a second pawl actuating arm connected respectively to said firstand second pawls, means including a cam driven by said shaft for drivingsaid first and said second pawl actuating arms in opposite phase in acyclic manner to move said pawls into and out of engagement with saidnotches in opposite phase to move said ratchet in incremental movementin one direction at a first speed, means cyclicly driven by said cam forcontrolling the movement of each of said pawls into engagement with oneof said notches for a portion of a cycle and for moving each of saidpawls out of engagement with said notches during a portion of saidcycle, each of said notches having substantially parallel sides for asubstantial portion of the depth thereof so as to retain said pawlstherein for a substantial portion of said cycle, and electromagneticmeans for selectively latching one of said pawl actuating arms away fromsaid cam following position to prevent the pawl associated with thelatched one of said arms from moving said ratchet during the cycle sothat said ratchet is driven at a second speed when said one actuatingarm is latched which is one-half said first speed at which said ratchetis driven when said one actuating arm is not latched.

References Cited in the file of this patent UNITED STATES PATENTS102,056 Sibley et a1 Apr. 19, 1870 305,752 Kellogg Sept. 30, 18842,343,549 Groghan Mar. 7, 1944 2,942,486 Beguin June 28, 1960 UNITEDSTATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 131,570 May5, 1964 Malcolm J. White It is' hereby certified. that error appears inthe above numbered patent requiring" correction and that the saidLetters Patent should read as corrected below Column 8, line 21, strikeout "away from said cam following position" and insert the same after"arms" in line 19, same column 8 Signed and sealed this 5th day'ofJanuary 1965.

(SEAL) Attesfz ERNEST w. SWIDE-R' EDWARD J. BRENNER Aittesting OfficerCommissioner of Patents

1. APPARATUS FOR PRODUCING INCREMENTAL MOTION FROM A ROTATING SHAFTCOMPRISING A SUBSTANTIALLY CIRCULAR RATCHET HAVING A PLURALITY OFNOTCHES THEREIN, A FIRST PAWL AND A SECOND PAWL ADAPTED TO ENGAGE SAIDNOTCHES, A FIRST PAWL ACTUATING ARM AND A SECOND PAWL ACTUATING ARMCONNECTED RESPECTIVELY TO SAID FIRST AND SECOND PAWLS, MEANS INCLUDING ACAM DRIVEN BY SAID SHAFT FOR DRIVING SAID FIRST AND SAID SECOND PAWLACTUATING ARMS IN OPPOSITE PHASE IN A CYLIC MANNER TO MOVE SAID PAWLSINTO AND OUT OF ENGAGEMENT WITH SAID NOTCHES TO ROTATE SAID RATCHET ININCREMENTAL STEPS IN ONE DIRECTION AT A FIRST SPEED, MEANS CYCLICLYDRIVEN BY SAID CAM FOR CONTROLLING THE MOVEMENT OF EACH OF SAID PAWLSINTO ENGAGEMENT WITH ONE OF SAID NOTCHES FOR A PORTION OF A CYCLE ANDFOR MOVING EACH OF SAID PAWLS OUT OF ENGAGEMENT WITH SAID NOTCHES DURINGA PORTION OF SAID CYCLE, EACH OF SAID NOTCHES HAVING SUBSTANTIALLYPARALLEL SIDES FOR A SUBSTANTIAL PORTION OF THE